Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors has continued to advance at a great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices.
Image sensors may implement dual conversion gain to obtain high dynamic range. The high dynamic range may be obtained by reading from pixels under low gain, then high gain, and then combining the two readouts. However, there may be a large difference in a reset level of the pixels in high and low conversion gain modes. While the difference in reset level may be compensated for using two comparators, the area for the comparator is doubled by having two comparators. Another way is to have two set of input stages of the comparator but parasitic capacitances within the comparators may affect frame rate, for example. Many techniques have been employed to mitigate these effects, but some of these methods may not entirely eliminate the effects.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.